Among Hispanic-American adolescents, acculturation to the United States culture has been identified as a risk factor for substance use. However, the complexities of acculturation processes and their influences on health risk behaviors remain only partially understood. Previous studies of adolescent acculturation and its consequences have not considered the family and peer contexts in which acculturation and ethnic identity formation occur. Understanding the social contexts of acculturation is important because most psychosocial risk factors for adolescent substance use involve peer and family influences. In immigrant families, multiple generations of family members are acculturating, typically at differing rates and with different patterns. Parent-child discrepancies in acculturation patterns could affect parental authority and parent-child communication, which in turn might influence the adolescents' selection of peers and activities and ultimately the adolescents' involvement in substance use. This study will examine adolescent acculturation patterns in the family context, the effects of parent-child acculturation discrepancies on family functioning, the effects of family functioning on peer social networks, the effects of social networks on adolescent substance use, and the moderating effects of community SES. The study will consist of a year of qualitative and pilot research, followed by a three-year longitudinal study and a year of qualitative research to contextualize the quantitative results. Over a three-year period, high school students in 4 predominantly Hispanic high schools in Southern California representing a range of SES (N=2000) will complete questionnaires about their acculturation patterns and family functioning. Social network analysis will be used to describe the structure of the adolescents' social networks and the prevalence of substance use among social network members. We will geocode the students' home addresses and the addresses of their social network members and use U.S. Census data to estimate the socioeconomic characteristics of the neighborhoods in which the adolescents likely spend time. Analyses will be conducted to understand the psychosocial mechanisms by which family acculturation patterns influence the risk of adolescent substance use, and the role of the social network and neighborhood contexts on those processes. The results will provide important information that can be used to develop more effective substance use prevention programs for adolescents in acculturating families.